tcmd: Daily Yields on Treasury Securities
Description
This data set contains daily 1 year, 3 year, 5 year, and 10 year
  yields on treasury securities at constant, fixed maturity.format
4 univariate time series tcm1yd, tcm3yd, tcm5yd,
  and tcm10yd and the joint series tcmd.source
U.S. Fed http://www.federalreserve.gov/Releases/H15/data.htmDetails
The yields at constant fixed maturity have been constructed by the
  Treasury Department, based on the most actively traded marketable
  treasury securities.  Daily refers to business days, i.e., weekends and holidays are
  eliminated.